Television amplifier system



July 8, 1941. sc gs s 2,248,560

TELEVIS ION AMPLIFIER SYSTEM Filed Oct. 7, 1933 2 Sheets-Sheet 1 Jnvem'op:

um 3W Jilly 1941- K. SCHLESINGER 2,248,560 TELEVISION AMPLIFIER SYSTEM Filed 001:. '7, 1938 2 Sheets-Sheet 2 Iza lb 112 Jnvenfop m im m Patented July 8, 1941 UNITED STATES FATE orrics TELEVISION AMPLIFIER SYSTEM Kurt Schlesinger, Berlin, Germany, assignor, by

mesne assignments, to Loewe Radio, Inc., a corporation of New York Application October 7, 1938, Serial No. 233,816 In Germany December 23, 1937 7 Claims.

Under their influence the amplification first in-- creases strongly towards low frequencies. At the same time there are considerable phase shifts. It is already known for the purpose of stabilising the system against fluttering effects to employ a series connection of the single anode-circuitsmoothing elements from stage to stage in the form of a chain system, and in a connection system of this kind a stabilisation, i. e. an automatic compensation of fluctuations in the supply lead,

takes place when the time constant of the anode circuit filter has the same value as the time constant of the grid circuit transmission elements. In this case the weakening of a potential fluctuation at the supply lead caused by each section of the anode circuit filter is just compensated by the amplification of the tube pertaining to the section, and the phase shift caused by the smoothing elements is compensated by anopposite phase shift on the part of the elements of the grid circuit 4, 5 (high pass).

It has been found, however, that this network feed with tuned periods of action operating very satisfactorily in itself undergoes considerable interference in the filter circuit and over the ampli- Y fier when the amplification of one of the ampli- 39 fying tubes is varied for regulating purposes. In this connection the regulation of the tubes can take place in itself by variation of the grid bias or of the screening grid potential, or better still by means of an intercepting grid disposed 'between screening grid and anode. In all of these which have the same time constant as the transmission elements between grid and anode, one or more stages being regulated by a distributing grid between screening grid and anode, the screening grid of this regulated tube or tubes is connected with the anode feed point of the preceding tube.

Accordingly, the screening grid current of one stage is not, as hitherto usual, conducted to the anode supply point of the own tube, but the screening grid current of the regulated stage is passed back to the preceding tube.

The invention is described more concisel in conjunction with the drawings. In Figs. 1 and 2 there are shown known connection systems for resistance amplifiers of the kind such as have been usual heretofore. Figs. 3 and 4 show by way of example embodiments of the connection system according to the invention.

Fig. 1 shows the fundamental arrangement of I the connection elements essential in conjunction with the subject matter of the present invention, the network for filtering the supply potential de rived from the supply lead 3 comprising the resistance l and the condenser 2. The resistance 6 is the anode resistance of the tube, and the condenser 4 and the resistance 5 are the transmission elements between the stage R and the next stage following thereon.

Fig. 2 shows a cascade arrangement for an amplifier connection system of this kind, this comprising the three tube stages R1, R2 and R3. The potential derived from the supply lead 3 is conducted by way of the series connected networks I, 2, la, 2a, lb, 21). The resistances 6, 1 and 8 are the anode resistances of the individual stages, and the coupling elements between anode and grid of the following stage are the condensers 4,

l0 and the resistances 5, II. The amplified output potential is supplied by way of the condenser l2. In this connection system, which is known per se, the middle stage R2 is furnished with a screening grid S, and furthermore this stage is capable of being regulated by means of a distributing grid 9 disposed between the screening grid S and the anode. By varying the potential at this intercepting grid 9 the power amplification ratio of the stage can be regulated. In the systems as shown in Figs. 1 and 2 the anode circuit smooth ing elements 1-, 2,1a, 2a lb and 2b serve to filter the arrangement in regard to fluctuations in potention (fluttering). As well known, best stabilisation occurs when the time constant of the anode circuit filter l, 2 has the same value as the time constant of the grid circuit transmission elements 4, 5 (see Figs. 1 and 2).

An amplifying system according to the present invention is illustrated by way of example in Fig. 3. This system is similar to the known system shown in Fig. 2, with the exception that in this system, in accordance with the invention, the screening grid S is connected to the anode supply point of the preceding stage R1. It is to be clearly recognised from this system that owing to this connection the low frequency potential variations which would develop at the anode circuit filter element 2 under the action of a tube RI can under certain conditions be compensated, viz. when the current drawn by the screening grid of the next tube R2 is weaker, exactly in the amplification ratio V, than the anode current of the tube B1. In this case, therefore, each of the single filter condensers 2, 2a. and 2b is nonoscillating in regard to the amplification. In principle the current equality condition for a desired stage can be adjusted by varying the bias of the screening grid or the anode. It is also possible by means of a distributing grid 9 provided between the screening grid and the anode to produce the correct distribution of current, and to return a fraction of the anode current to the screening grid, should the natural screening grid current not be sumcient. By the inclusion of a parallel resistancecondenser element l3, l4 it is possible if necessary, to reduce the Screening grid current, and accordingly also the slow fluctuations of the same if by means of the parallel condenser l4 the screening grid is maintained constant for all medium and high frequencies.

In practice it has been found that the adjustment of the screening grid equilibrium is not very critical, and that in particular any lack of balance of the screening grid condition can be very well compensated by varying the values with respect to the filter circuit elements I, 2. Simple theory results in the following values for the anode filter in conjunction with the tube transconductance to the screen S, in which connection there can merely be concerned a rough indication of the order of magnitude.

Assume an alternating voltage e at the anode of tube R1. If anode resistance 6 is neglected (as it may be at low frequencies) and omit resistance I, the alternating voltage 6 would cause a current 6110C: to flow in condenser 2. At the same time it causes current ey'wCr to flow in condenser 4 when the impedance of condenser 4 is large as compared to resistance 5, as would be the case at low frequencies. Then the grid voltage of tube R2 is eiwC4Rs and if S is the transconductance to the screen of the tube, the current from the screen is e9wC4RsS. This also flows into condenser 2 and being of opposite sign will neutralize the first current eywCz if C4R5S=C2.

When the product of transconductance to the screen, expressed in mhos, and the resistance I, expressed in ohms, is taken as unity then R1S=l and When this condition exists then C4Rs=C2R1.

The time constant of the grid circuit, IQ, is

then C4R5 and is equal to the time constant of the anode filter, TA, which is CZRI. Oscillographically determined:

C4=0.1;if R=0.3M9 Tg=0.03SC. 02:60 R1=500Q TA=0.03SeC.

It is found in practice that in the screening grid connection according to the invention as shown in Fig. 3 there is possible a regulation of the power amplification ratio at the intercepting grid of one of the tubes, without the occurrence of distortions and without variation of any kind in the low frequency characteristics of the amplifier. It is even sufficient in practice to employ the connection of the screening grid according to the invention only in one stage, viz.

in the interception grid regulating stage, and to use the remaining tubes in the known normal connection according to Fig. 2, i. e. to feed the screening grid from the own anode potential point. This can be understood, as in the case of a stage R2 regulated by interception grid in accordance with Fig. 3 the screening grid current increases considerably at the expense of the anode current if the amplification of the tube is to be smaller. For the same reason a regula tion by the control grid is not without distortion, as in this case the screening grid compensation of the distortion according to the invention does not take place.

The compensation of the distortion in accordance with the invention functions properly only in the case of interception grid regulation, but not with screening grid or control grid regulation. There is also the fact that interception grid regulation has the advantage of not introducing curvature of the characteristic and of operating in noiseless and wattless fashion and of being outside of the amplifier circuit.

At the end of the supply lead the connection of the screening grid according to the invention cannot be continued further. There also occurs there a reflection of fluctuation waves which have penetrated into the beginning of the lead, more particularly charges of the final filter condenser 2 emanating from the end stage. A connection system of this kind exhibits a tendency to flutter when the tubes are more than 4 in number. These interferences all disappear when the final filter condenser, i. e. 2 is steadied in regard to potential. To accomplish this there is employed, according to an additional feature of the invention, a special auxiliary tube, which is connected with its anode to the condenser 2. A connection system of this kind is illustrated in Fig. 4, which differs from the connection system shown in Fig. 3 by the additional tube stage IS. The object of this connection system is to introduce into the condenser 2 a current which is exactly of equal amount and. opposite to the current reaching the condenser from the network or from the remaining amplifying stages R1-R3. For this purpose the control grid of the tube I5 is connected by way of an adjustable potentiometer l6 and the condenser I! with the preceding feed point at 2:1. These coupling elements It and I1 are so selected that a tight coupling is obtained for very low frequencies (condenser l1 large, resistance l6 high). It is then possible at the resistance I5 to adjust a tapping in such fashion that fluctuations in potential (fluttering) no longer occur in a connection system of this kind.

I claim:

1. In a resistance-capacity coupled amplifier arrangement, more particularly for television purposes, comprising several amplifier tubes, anode-resistances, coupling-condensers and gridleak resistances between said tubes, a feed line circuit connected to the anode-circuits of said tubes via resistance-condenser filter-networks arranged in series connection, each one of which is associated to the anode circuit of one of said tubes, and has the same time constant as the resistance-condenser-coupling between. said tubes, the use of one or more screening grid tubes including besides the screening grid an intercepting grid between screening grid and anode for regulating the amplification degree, said screening grid being connected to the anode circuit of the preceding amplifier tube.

2. In a resistance-capacity coupled amplifier arrangement, more particularly for television purposes, comprising several amplifier tubes, anode-resistances, coupling-condensers and gridleak resistances between said tubes, a feed line circuit connected to the anode-circuits of said tubes via resistance-condenser filter-networks arranged in series connection, each one of which is associated to the anode circuit of one of said tubes, and has the same time constant as the resistance-condensercoupling between said tubes, the use of one or more screening grid tubes including besides the screening grid an intercepting grid between screening grid and anode for regulating the amplification degree, said screening grid being connected to the anode circuit of the preceding amplifier tube, via a resistance shunted by a condenser, said resistance being thus dimensioned that the current fiowing through the screening grid circuit compensates the detrimental potential fiuctuations at the filter-condenser associated to said preliminary amplifier tube.

3. A resistance-capacity coupled amplifier arrangement, more particularly for television purposes, comprising several screening grid tubes including besides the screening grid an intercepting grid between said screening gridand the anode for regulating the amplification degree, coupling means between said tubes, a feed line circuit connected to the anode circuits of said tubes via resistance-condenser filter networks arranged in series connection, each one of which is associated to the anode circuit of one of said tubes and has the same time constant. as the resistanceand condenser couplingbetween said tubes, each one of the screening grids of all said tubes being connected to the anode-circuit of its preliminary tube.

4. A resistance capacity coupled amplifier arrangcment, more particularly for television purposes, comprising several screening grid tubes including besides the screening grid an intercepting grid between said screening grid and the anode for regulating the amplification degree, a phase-reversing device, coupling means between said tubes, a feed line circuit connected to the anode circuits of said tubes via resistance-condenser filter networks arranged in series connection, each one of which is associated to the anode circuit of one of said tubes and has the same time constant as the resistanceand condenser coupling between said tubes, each one of the screening grid of all said tubes being connected to the anode-circuit of its preliminary tube, said phase reversing device being an electronic tube including at least anode, control grid and cathode, said control grid being connected by means of a variable potentiometer resistance and a condenser to the filter condenser electrode associated to the anode circuit of the second amplifier tube, and the anode of said phase reversing tube being connected to the filter-condenser electrode associated to the first amplifier tube.

5. A resistance-capacity coupled amplifier arrangement, more particularly for television purposes, comprising several screening grid tubes including besides the screening grid an intercepting grid between said screening grid and the anode for regulating the amplification degree, a phase-reversing device, coupling means between said tubes, a feed line circuit connected to the anode circuits of said tubes via resistance-condenser filter-networks arranged in series connection, each one of which is associated to the anode circuit of one of said tubes and has the same time constant as the resistanceand condenser coupling between said tubes, each one of the screening grid of all said tubes being connected via a resistance shunted by a condenser to the anode-circuit of its preliminary tube, said resistance being thus dimensioned that the current flowing through the screening grid circuit compensates the detrimental potential fluctuations at the filter condenser associated to said preliminary amplifier tube, said phase reversing device being an electronic tube including at least anode, control grid and cathode, said control grid being connected by means of a variable potentiometer resistance and a condenser to the filter condenser electrode associated to the anode circuit of the second amplifier tube, and the anode of said phase reversing tube being connected to the filtercondenser electrode associated to the first amplifier tube.

6. A resistance-capacity coupled amplifier comprising a plurality of amplifier tubes of which at least one is a screen grid tube, a source of voltage for energizing said tubes, a filter circuit for filtering said supply voltage, said filter circuit comprising a plurality of series connected resistance elements and a plurality of parallelly connected capacity elements connected intermediate the several resistance elements, a connection between the output electrode of the first of said amplifier tubes and the junction of the last of said filter condensers and resistance elements, said connection including an output load resistor for said tube, a connection between the output electrode of the second of said amplifier tubes and the junction of the last and second last filter resistance and the second last filter capacity elements, said last-named connection including a load resistor for said second tube, means for applying signals to the control electrode of the first of said tubes, 2. connection for energizing the input circuit of said second tube by the output energy of the first tube, said connection including a coupling condenser and a grid leak resistor, said second tube being a screen grid tube and having a connection from the screen electrode of said tube to the terminal of the load resistor of said first tube which connects to the said filter circuit.

'7. The amplifier circuit claimed in claim 6, comprising in addition a parallelly connected resistance and capacity circuit connected serially intermediate the screen electrode of the second tube and the connection point thereof to the output load resistor of said first tube.

KURT SCI-ILESINGER. 

